The Senate struggled Thursday to prevent a corporate tax bill (search) that aims to end an escalating trade fight with Europe from falling victim to a political clash over unemployment benefits (search).

Senate Majority Leader Bill Frist, R-Tenn., said senators failed to bridge their differences over a Democratic amendment that would extend unemployment benefits for 13 weeks. Frist said the Senate would vote Monday to cut off debate on the unemployment issue and force Democrats to drop other unrelated amendments.

"I want to bring this to a close," he said.

To end debate on the unemployment issue, 60 of 100 senators must vote in favor of the motion.

The Senate's top tax writer said the bill could be dead for the year if Monday's vote fails.

"I won't ask that the bill be brought up again this year," Senate Finance Committee Chairman Charles Grassley, R-Iowa, said in written statement.

Some U.S. exports face punitive tariffs imposed by the European Union (search) that ratchet up 1 percentage point each month until the bill becomes law. The tariffs are punishment for a $5 billion annual tax break for U.S. exporters that trade regulators declared an illegal export subsidy. The corporate tax bill eliminates the offending tax break.

The sanctions started at 5 percent in March and can increase to as much as 17 percent. They climbed to 7 percent this month and would reach 15 percent in January.

Grassley said Sen. Maria Cantwell, D-Wash., put the tax bill "in serious jeopardy" by insisting the Senate immediately debate and vote on her amendment to extend unemployment benefits.

Cantwell said Republicans have no good reason to prevent her from trying to attach the unemployment benefit extension to the corporate tax bill. "Is it because they're afraid it's going to win?" she said.

Grassley called the effort "political chicanery."

"Perhaps a perceived edge in this year's congressional election is more important to some than actually legislating real solutions to America's economic problems," he said.

Sen. Edward Kennedy, D-Mass., has joined Cantwell to push for longer unemployment benefits. He said unemployment is a real economic problem.

"We have shredded the safety net for hardworking Americans," he said.

Kennedy also said Democrats have no intentions of backing down.

"This is a defining issue for the Democratic Party," he said. "There is no issue like overtime, unemployment and minimum wage that are defining issues for the Democratic Party, and if people aren't going to stand for workers ... then I don't understand who they stand for."